For nearly a thousand years, WiFi sync between my phone (currently running 10.3.2) and Mac mini (running Sierra presently) worked just fine. Suddenly last week, it stopped. Syncing with a USB cable works fine. Unplug the cable, and you get the grey sync button and the message in the title. I have tried all of the following multiple times and in varying orders. None of it has helped: Restarting iTunes Rebooting the computer Rebooting the phone Connecting with a cable, unchecking the "wifi sync" checkbox, applying that, then re-checking it and applying that Reinstalling iTunes signing out of iCloud on the phone (and back in) signing out of iCloud on the mac (and back in) killing usbmuxd and letting it restart killing iTunes helper and restarting it Changing the name of the computer and toggling the wifi sync checkbox in iTunes. Switching between Ethernet and WiFi connectivity on the mac (both networks are bridged with an AirPort express). It's 2017. Why is this just not a done deal by now?!